R Dhamodharan

A new, super water-absorbing, material is synthesized by the reaction between chitosan, EDTA and urea and named as CHEDUR. CHEDUR is probably formed through the crosslinking of chitosan molecules (CH) with the EDTA-urea (EDUR) adduct that is formed during the reaction. CHEDUR as well as the other products formed in control reactions are characterized extensively. CHEDUR exhibits a very high water uptake capacity when compared with chitosan, chitosan-EDTA adduct, as well as a commercial diaper material. A systematic study was done to find the optimum composition as well as reaction conditions for maximum water absorbing capacity. CHEDUR can play a vital role in applications that demand the rapid absorption and slow release of water such as agriculture, as a three in one new material for the slow release of urea, water and other metal ions that can be attached through the EDTA component. The other potential advantage of CHEDUR is that it can be expected to degrade in soil based on its chitosan backbone. The new material with rapid and high water uptake could also find potential applications as biodegradable active ingredient of the diaper material.

The preparation of super water-absorbing hydrogel through the hydrothermal reaction of a mixture of chitosan (CH), itaconic acid (IT) and urea (UR), all of which are sustainable materials, is reported. The structure of the new material, CHITUR, is established by 13C solid-state NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction analysis (PXRD) and thermogravimetric analysis (TGA). It consists predominantly of unmodified CH and a small fraction of ionotropically cross-linked CH involving ITUR salt as cross-links. The structure of the CHITUR was independent of the composition of IT, UR as well as water content used in the preparation, while the morphology differed significantly. CHITUR exhibited high water and aqueous sodium chloride (0.01 w/v%) absorption. Compared to all the CHITUR preparations, the one with CH:IT:UR of 1:3:3 (all by weight) and 7.5 mL of water per gram of chitosan provided high water absorption, but when the CH:water ratio is increased for this composition of CH:IT:UR, water absorption did not increase significantly. The best water uptake of about 100 g/g (10,000%) was obtained with CHITUR prepared with the following weigh ratio of reactants, namely CH:IT:UR of 1:3:3 with the chitosan:water weight ratio being 1:7.5. In preliminary studies, CHITUR was observed to be suitable for hydroponic growth of seeds.

In this work, the synthesis and characterization of a new polymer, natural rubber-g-chitosan, from biopolymers available in nature is reported. In this process, soft and amorphous natural rubber (NR) is converted into a relatively more dimensionally stable new polymer (glass transition temperature changes from −68 to +94.5 °C), with versatile solubility in a variety of common organic solvents. For this purpose, mild epoxidation of NR is carried out to provide a reactive handle for the grafting of chitosan. Thus, chitosan-grafted natural rubber with different chitosan loading have been synthesized and characterized. The characterization of the new polymers revealed that the grafting process resulted in enhanced glass transition temperature in comparison to NR, remarkable improvement in thermal stability in comparison to NR and chitosan and the much needed solubility for the chitosan component, which is otherwise insoluble in common organic solvents. The NR-g-chitosan is fully amorphous in the solid state, similar to NR. These value-added characteristics promise the utility and processability of the newly synthesized materials in adhesives, packaging industries and in many other areas where natural rubber and chitosan are vitally employed.

A new superabsorbent with maximum water absorption capacity of ∼1250 g/g is prepared by hydrothermal synthesis from sustainable and biodegradable resources such as chitosan, citric acid and urea (denoted as ‘CHCAUR’). CHCAUR is characterized extensively by various analytical techniques such as PXRD, SSNMR, FTIR, and TGA. Pure and saline water absorption study showed that CHCAUR could be a better adsorbent compared to the super absorbent polymer (SAP) used in commercial diaper material. The mechanism of water absorption is shown to arise out of a combination of electrostatic attraction of water to the ionic crosslinks and the presence of macropores as well as undulated surface due to the formation of nanofibrous bundles. When applied to soil CHCAUR was found to decrease water evaporation rate significantly.

Biocompatible hydrogels were prepared by mixing aqueous-acidic solution of chitosan with alkali lignin, a major by-product of the paper producing industries, for the first time, by sustainable means. Electrostatic interactions between the phenoxide groups in lignin and the ammonium groups on the chitosan backbone were found to be responsible for the ionotropic cross-linking. These gels were non-toxic to Mesenchymal stem cells, in vitro, and to zebrafish up to 100 μg/ml, in vivo. In addition, these gels provided a conducive surface for cell attachment and proliferation, making it suitable for application as scaffolds in tissue engineering. In presence of the hydrogel, NIH 3T3 mouse fibroblast cells showed good cell migration characteristics suggesting that the gel might be suitable for wound healing application. The chitosan-alkali lignin gelation system was further capable of removing ferric ions from contaminated water by way of complexation and coagulation. Cross-linked films of chitosan and alkali lignin could also be prepared by simply immersing chitosan films into a solution of alkali lignin. Alkali lignin was observed to diffuse into the chitosan “crystal”, forming electrostatic cross-links between the chitosan chains. The choice of lignin, in comparison to the other ionotropic cross-linkers for chitosan, makes the cross-linking system, inexpensive and sustainable.